I wouldn't be scared of the Iron Gall inks (Scabiosa and Salix). They are a modern formula and not as reactive/corrosive/clog-prone as some of the ancient recipes. Ordinary fountain pen hygiene and common sense is all that's needed. Don't mix these inks with others, be sure to thoroughly clean the pen when switching inks, and don't leave it in a pen for months at a time. That same advice should apply to any inks, not just iron gall. I would be somewhat reluctant to use it in a particularly valuable, rare, vintage pen, but almost any modern writing instrument should not have issues. I have both Scabiosa and Salix, use them regularly in numerous pens, and have had zero problems.

Last year I had Salix in a Nemosine Singularity Demonstrator inked with Salix and a Goulet 2-tone 1.5 Stub Nib for close to 9 months, cleaned it out completely one day, and not a single stain or issue on the nib or converter.

As you said, the modern cold press formulation while not as deep as some of the other iron gall formulations are still rather safe for most fountain pens, they just require a tiny bit more care such as emptying out and refilling least once a month or so (since I do all my filling from a sample vial, it's easy to expel into the vial, shake it up a little and refill) so that the ink is not so evaporated.

I find Salix to be an excellent dryer ink for my vintage pens with semi-flex nibs, next to no feathering. Presently it's in a 1956 Pelikan 400NN with a 14K Semi-Flex EF (the nib unit itself has a hard rubber collar instead of a steel one like the newer nib units), before that I primarily used it in a 1940s Eversharp Skyline with a similar 14K Semi-Flex EF. No problems, and it was generally the best ink for flow and lack of feathering when dealing with wetter nib/feeds.

Am I the only one who found Salix to be quite a slow drying ink? :) Ok, it was probably just a matter of paper, or even environment. I should really stop saying anything about dry times, I never got them right!

I just wanted to add that I can vouch for the safety of R&K iron gall inks with 14k white gold nibs (few available nowadays, but my Hastil has one), rhodium plated gold ones, both 14k and 18k.

One last thing: you have one really sweet taste for vintage pens Karl! I've never been into vintage pens too much, but I've recently started appreciating the flex that only vintage stuff can give. I've yet to own a real vintage flex pen myself, as I'm still trying to decide which model would be better suited for me. Just consider that it took me a couple of weeks of personal testing (thanks to a couple of friends) of both the standard Vanishing Point and the Décimo, before deciding to go for the latter. And then another week to choose the color. I'm afraid my first step into flex vintage pens will require longer preparation than the first step on the moon. ;)

Depends on the wetness of the nib and absorbency of the paper. R&K Salix is a dryer ink, but it also resists feathering and bleeding very well, as a result if you put down a nice wet thick line, the ink that remains atop is going to take a while to dry as opposed to some inks that'll feather like hell but will be dried faster due to spreading more quickly into the paper.

I find it nice in a wetter pen especially vintage flex, makes the writing a bit more controllable on most paper types. But most of mine starts around an EF/F line.

I found Scabiosa to have (understandably) the same properties, despite it having slightly faster drying times. The fraction of the ink that gets instantly absorbed ends up being a nice ancient looking light pink-purple, with notes of grey that gets more prominent as the ink dries and the iron gall composition oxidizes. This part of the ink dries almost instantly with zero feathering or bleed through. When I end a line, on the other hand, the viscosity of the ink manages to drive a nice "blob" (sorry for this extremely technical term :) of ink out of the nib, as long as the feed is wet enough. These parts have a nice, deep and saturated purple, with the usual grey notes that later become more prominent. Unfortunately this unabsorbed sections dries much slower, but I would never trade this kind of shading with faster drying times!

Oh, about vintage flex pens, one starting from EF and going all the way up to a nice BB, (or even BBB) would likely end up in my top 4! I'm waiting for a flea market that is kept every month where I live. Back in the day (when I didn't particularly like vintage pens) I saw a decent number of vintage fountain pens, mostly Waterman and Parker, but also some with what I would come to know as the Mabie Todd logo. I hope I'll something interesting, I just added a R&K Blu Mare to my collection, as I recently went out of Pelikan 4001 Turquoise, so I might give both the pen (if I find it) and the ink a combo test run.